This invention relates to the field of the decoding of composite television signals, and more particularly to the field of an improved architecture for a decoder of composite television signals such that the performance is improved while the cost of manufacturing is simultaneously reduced.
A composite television signal consists of a main carrier of luminance information onto which a quadrature modulated subcarrier containing two components of quadrature modulated chrominance has been added. A decoder, at a minimum, must be able to separate the carrier and subcarrier signals, to produce a luminance output based on the content of the main carrier, and quadrature demodulate the subcarrier to produce two chrominance components.
To be commercially viable, a decoder should also perform dc restoration of the input and output, blanking processing, including output sync signal addition, internal test signal generation, superior filtering, local and remote control of user adjustable parameters, matrix conversion to at least some and preferably all of the standard and nonstandard component formats, have a variable electrical length to ease system timing requirements, and contain features which aid in the adjustment and troubleshooting of the decoder itself.
Referring to FIG. 1, a typical prior art television signal decoder performs blanking on the separated red, green and blue signals immediately prior to sending them out as outputs. Test signal generation is also typically switched into the component red, green and blue color signals, just before sync and blanking processing. It would be desirable to build a television signal decoder with an improved architecture that performs these same functions more efficiently and effectively than they have been performed in the prior art.